From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 388B8C433E0 for ; Thu, 2 Jul 2020 13:07:23 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0CA51207CD for ; Thu, 2 Jul 2020 13:07:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0CA51207CD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=tls.msk.ru Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37220 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jqyvy-0001WH-9T for qemu-devel@archiver.kernel.org; Thu, 02 Jul 2020 09:07:22 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56836) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jqyvG-0000qa-SK for qemu-devel@nongnu.org; Thu, 02 Jul 2020 09:06:38 -0400 Received: from isrv.corpit.ru ([86.62.121.231]:41389) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jqyvE-0003O1-Oc for qemu-devel@nongnu.org; Thu, 02 Jul 2020 09:06:38 -0400 Received: from tsrv.corpit.ru (tsrv.tls.msk.ru [192.168.177.2]) by isrv.corpit.ru (Postfix) with ESMTP id 08C7840098; Thu, 2 Jul 2020 16:06:33 +0300 (MSK) Received: from [192.168.177.99] (mjt.vpn.tls.msk.ru [192.168.177.99]) by tsrv.corpit.ru (Postfix) with ESMTP id C56F46D; Thu, 2 Jul 2020 16:06:32 +0300 (MSK) Subject: Re: [PATCH] Makefile: Compute libraries for libqemuutil.a and libvhost-user.a To: Christophe de Dinechin , Stefan Hajnoczi References: <20200616161814.891053-1-dinechin@redhat.com> <20200623144415.GP36568@stefanha-x1.localdomain> From: Michael Tokarev Message-ID: Date: Thu, 2 Jul 2020 16:06:32 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: none client-ip=86.62.121.231; envelope-from=mjt@tls.msk.ru; helo=isrv.corpit.ru X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/02 09:06:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Spam_score_int: -68 X-Spam_score: -6.9 X-Spam_bar: ------ X-Spam_report: (-6.9 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_HELO_NONE=0.001, SPF_NONE=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 01.07.2020 12:12, Christophe de Dinechin wrote: .. >>> # Build libraries >>> >>> +libqemuutil.a-libs += $(call extract-libs, $(util-obj-y) $(trace-obj-y) $(stub-obj-y)) >>> +libvhost-user.a-libs += $(call extract-libs, $(libvhost-user-obj-y) $(util-obj-y) $(stub-obj-y)) .. >> Another thing I wonder about: the purpose of the .a files is to compile >> all object files and only link those .o files needed by the program >> (i.e. a subset of the .a file). > > I believe that what you are saying is that by passing the required libraries > automatically, the binaries that use libqemuutil.a will inherit undesired > ldd dependencies. Indeed, a quick experiment shows that if you pass a -l > option, the library dependency is recorded even if no symbol in that library > is used. I saw no obvious linker option to address that. There's --as-needed and --no-as-needed ld flag (used with cc as -Wl,--as-needed), which is designed for this very case. JFYI. /mjt